1. Field of the Invention
The present invention relates to a stage apparatus, an exposure apparatus, and a device manufacturing method.
2. Description of the Related Art
Japanese Patent Laid-Open No. 2004-79639 discloses a conventional alignment stage apparatus which mounts a repulsion magnet unit.
FIG. 11A is a perspective view showing an alignment stage apparatus according to a prior art. In this alignment stage apparatus, a base guide is fixed on a main body base, and a stage 103 which mounts a processing object 102 is supported to be movable in one axial direction with respect to the base guide. A bearing inserted between the upper surface of the base guide and the lower surface of the stage 103 regulates the orientation of the stage 103. Linear motor movable elements 105 are fixed on the two sides of the stage 103. A linear motor stator 106 faces the linear motor movable element 105 in a noncontact manner, and is fixed on the main body base. The position of the stage 103 is measured by irradiating a reflection mirror with light from a laser interferometer.
This alignment stage apparatus comprises repulsion magnet units shown in FIG. 11B. Repulsion movable elements 133 each including a movable magnet holder 131 and movable magnet 132 are fixed on the front and back sides of the stage 103. The movable magnet 132 is a plate-like permanent magnet magnetized in the vertical direction. In this prior art, the upper surface of the movable magnet 132 is magnetized into an N pole. The repulsion movable element 133 interacts with a repulsion stator 135 arranged on the base guide 101 to apply a repulsive force to the stage 103, thereby accelerating or decelerating it.
This repulsion magnet unit has a structure in which upper and lower magnets 137 sandwich the respective pole faces of the movable magnet 132 from both sides so as to cancel a repulsive force in the direction in which they face each other. The repulsion stators 135 which apply accelerating and decelerating forces to the stage 103 are fixed on the base guide in correspondence with the repulsion movable elements 133. The repulsion stator 135 is set at each end of the stroke region of the stage 103.
The interval between the upper and lower magnets 137 is slightly wider than the thickness of the movable magnet 132, while the inner interval between two side yokes 138 is wider than the width of the movable magnet 132. The movable magnet 132 can be inserted into a hole in a non-contacting manner, which is formed among the pair of upper and lower magnets 137 and two side yokes 138.
When the repulsion movable element 133 is present at a dotted position, it receives a repulsive force in the direction indicated by an arrow A. As the repulsion movable element 133 is pushed out from the dotted position upon receiving the repulsive force in the direction indicated by the arrow A, the magnitude of the repulsive force decreases. When the repulsion movable element 133 separates from the repulsion stator 135 to a certain extent, the magnitude of the repulsive force becomes zero. Since the stage 103 has already been accelerated to a maximum speed and is guided by the bearing, it moves to the opposite side while keeping the speed at this time.
The linear motor movable element 105 produces a force so that the stage 103 keeps a constant speed against deceleration attributed to the air resistance and bearing. The kinetic energy of the stage 103 is conserved until the repulsion movable element 133 on the opposite side of the stage 103 interacts with the repulsion stator 135 at the other end. Hence, the speed of the repulsion movable element 133 on the opposite side of the stage 103 also becomes zero while it is inserted into the repulsion stator 135 at the other end by the same amount of insertion as that at the dotted position shown in FIG. 11B.
In recent years, a stage apparatus mounted in an exposure apparatus is required to drive at a higher acceleration to improve the throughput, while it is desired to perform alignment with a higher accuracy to increasingly micropattern semiconductors. Under the circumstances, there is proposed a stage apparatus which has a configuration of coarse and fine motions, and which includes a coarse motion stage for long stroke movement and a fine motion stage for accurate alignment.
Unfortunately, the conventional alignment stage apparatuses have a demerit that a linear motor for a fine motion stage generates heat in large quantities upon driving a coarse motion stage at high accelerations. The linear motor for the fine motion stage utilizes a Lorentz force, so it is excellent in response and vibration isolation characteristics, but generates heat in relatively large quantities as compared with other actuators. The heat generation is problematic especially in acceleration and deceleration. In scanning exposure, the coarse motion stage accelerates first. As the coarse motion stage reaches a maximum speed, exposure is performed while it travels at a constant speed. After the exposure, the coarse motion stage decelerates. This sequence is repeated. The fine motion linear motor must apply a thrust having a magnitude defined by “(the mass of the fine motion stage)×(the acceleration of the fine motion stage)” to the fine motion stage in accelerating and decelerating the coarse motion stage. Upon accelerating or decelerating the coarse motion stage, the fine motion linear motor generates heat and then the ambient air fluctuates to result in a measurement error of an interferometer, or the fine motion stage deforms due to heat generated by the fine motion linear motor. This deteriorates the alignment accuracy of the fine motion stage. Another problem is that the acceleration of the coarse motion stage must be limited to suppress heat generation by the fine motion stage, resulting in a decrease in throughput.
An electromagnetic coupling using a force produced by an electromagnet is also proposed as a means for transmitting accelerating and decelerating forces between the coarse motion stage and the fine motion stage. However, the electromagnetic coupling requires an enormous amount of electric power to transmit an accelerating force produced in greatly accelerating the coarse motion stage, resulting in an increase in the amount of heat generation. Another problem is that the shape of the fine motion stage becomes complicated. This makes it difficult to raise the frequency range of the servo gain.